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><TD
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>Chapter 29. <TT
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>/dev</TT
> and <TT
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>/proc</TT
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><DIV
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><H1
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><A
NAME="PROCREF1"
></A
>29.2. <TT
CLASS="FILENAME"
>/proc</TT
></H1
><P
><A
NAME="PROCREF2"
></A
></P
><P
>The <TT
CLASS="FILENAME"
>/proc</TT
> directory
	is actually a pseudo-filesystem.  The files in <TT
CLASS="FILENAME"
>/proc</TT
> mirror currently running
	system and kernel <A
HREF="special-chars.html#PROCESSREF"
>processes</A
>
	and contain information and statistics about them.</P
><P
>         <TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
><TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/devices</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>Character devices:
   1 mem
   2 pty
   3 ttyp
   4 ttyS
   5 cua
   7 vcs
  10 misc
  14 sound
  29 fb
  36 netlink
 128 ptm
 136 pts
 162 raw
 254 pcmcia

 Block devices:
   1 ramdisk
   2 fd
   3 ide0
   9 md</TT
>



<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/interrupts</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>           CPU0       
   0:      84505          XT-PIC  timer
   1:       3375          XT-PIC  keyboard
   2:          0          XT-PIC  cascade
   5:          1          XT-PIC  soundblaster
   8:          1          XT-PIC  rtc
  12:       4231          XT-PIC  PS/2 Mouse
  14:     109373          XT-PIC  ide0
 NMI:          0 
 ERR:          0</TT
>


<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/partitions</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>major minor  #blocks  name     rio rmerge rsect ruse wio wmerge wsect wuse running use aveq

    3     0    3007872 hda 4472 22260 114520 94240 3551 18703 50384 549710 0 111550 644030
    3     1      52416 hda1 27 395 844 960 4 2 14 180 0 800 1140
    3     2          1 hda2 0 0 0 0 0 0 0 0 0 0 0
    3     4     165280 hda4 10 0 20 210 0 0 0 0 0 210 210
    ...</TT
>



<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/loadavg</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>0.13 0.42 0.27 2/44 1119</TT
>



<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/apm</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>1.16 1.2 0x03 0x01 0xff 0x80 -1% -1 ?</TT
>



<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/acpi/battery/BAT0/info</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>present:                 yes
 design capacity:         43200 mWh
 last full capacity:      36640 mWh
 battery technology:      rechargeable
 design voltage:          10800 mV
 design capacity warning: 1832 mWh
 design capacity low:     200 mWh
 capacity granularity 1:  1 mWh
 capacity granularity 2:  1 mWh
 model number:            IBM-02K6897
 serial number:            1133
 battery type:            LION
 OEM info:                Panasonic</TT
>
 
 
 
<TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>fgrep Mem /proc/meminfo</B
></TT
>
<TT
CLASS="COMPUTEROUTPUT"
>MemTotal:       515216 kB
 MemFree:        266248 kB</TT
>
         </PRE
></FONT
></TD
></TR
></TABLE
>
      </P
><P
>Shell scripts may extract data from certain of the files in
         <TT
CLASS="FILENAME"
>/proc</TT
>.

	   <A
NAME="AEN19180"
HREF="#FTN.AEN19180"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>FS=iso                       # ISO filesystem support in kernel?

grep $FS /proc/filesystems   # iso9660</PRE
></FONT
></TD
></TR
></TABLE
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>kernel_version=$( awk '{ print $3 }' /proc/version )</PRE
></FONT
></TD
></TR
></TABLE
></P
><P
><TABLE
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BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>CPU=$( awk '/model name/ {print $5}' &#60; /proc/cpuinfo )

if [ "$CPU" = "Pentium(R)" ]
then
  run_some_commands
  ...
else
  run_other_commands
  ...
fi



cpu_speed=$( fgrep "cpu MHz" /proc/cpuinfo | awk '{print $4}' )
#  Current operating speed (in MHz) of the cpu on your machine.
#  On a laptop this may vary, depending on use of battery
#+ or AC power.</PRE
></FONT
></TD
></TR
></TABLE
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# get-commandline.sh
# Get the command-line parameters of a process.

OPTION=cmdline

# Identify PID.
pid=$( echo $(pidof "$1") | awk '{ print $1 }' )
# Get only first            ^^^^^^^^^^^^^^^^^^ of multiple instances.

echo
echo "Process ID of (first instance of) "$1" = $pid"
echo -n "Command-line arguments: "
cat /proc/"$pid"/"$OPTION" | xargs -0 echo
#   Formats output:        ^^^^^^^^^^^^^^^
#   (Thanks, Han Holl, for the fixup!)

echo; echo


# For example:
# sh get-commandline.sh xterm</PRE
></FONT
></TD
></TR
></TABLE
></P
><P
>+</P
><P
><TABLE
BORDER="0"
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><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>devfile="/proc/bus/usb/devices"
text="Spd"
USB1="Spd=12"
USB2="Spd=480"


bus_speed=$(fgrep -m 1 "$text" $devfile | awk '{print $9}')
#                 ^^^^ Stop after first match.

if [ "$bus_speed" = "$USB1" ]
then
  echo "USB 1.1 port found."
  # Do something appropriate for USB 1.1.
fi</PRE
></FONT
></TD
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></P
><DIV
CLASS="NOTE"
><P
></P
><TABLE
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WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/note.gif"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>It is even possible to control certain peripherals with commands
	  sent to the <TT
CLASS="FILENAME"
>/proc</TT
> directory.

          <TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>	  <TT
CLASS="PROMPT"
>root# </TT
><B
CLASS="COMMAND"
>echo on &#62; /proc/acpi/ibm/light</B
>
          </PRE
></FONT
></TD
></TR
></TABLE
>

	  This turns on the <EM
>Thinklight</EM
> in certain models
	  of IBM/Lenovo Thinkpads. (May not work on all Linux distros.)</P
><P
>Of course, caution is advised when writing to <TT
CLASS="FILENAME"
>/proc</TT
>.</P
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="PROCRUNNING"
></A
></P
><P
>The <TT
CLASS="FILENAME"
>/proc</TT
> directory
	   contains subdirectories with unusual numerical
	   names.  Every one of these names maps to the <A
HREF="internalvariables.html#PPIDREF"
>process ID</A
> of a currently running
	   process.  Within each of these subdirectories, there are
	   a number of files that hold useful information about the
	   corresponding process.  The <TT
CLASS="FILENAME"
>stat</TT
> and
	   <TT
CLASS="FILENAME"
>status</TT
> files keep running statistics
	   on the process, the <TT
CLASS="FILENAME"
>cmdline</TT
> file holds
	   the command-line arguments the process was invoked with, and
	   the <TT
CLASS="FILENAME"
>exe</TT
> file is a symbolic link to the
	   complete path name of the invoking process. There are a few
	   more such files, but these seem to be the most interesting
	   from a scripting standpoint.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="PIDID"
></A
><P
><B
>Example 29-3. Finding the process associated with a PID</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# pid-identifier.sh:
# Gives complete path name to process associated with pid.

ARGNO=1  # Number of arguments the script expects.
E_WRONGARGS=65
E_BADPID=66
E_NOSUCHPROCESS=67
E_NOPERMISSION=68
PROCFILE=exe

if [ $# -ne $ARGNO ]
then
  echo "Usage: `basename $0` PID-number" &#62;&#38;2  # Error message &#62;stderr.
  exit $E_WRONGARGS
fi  

pidno=$( ps ax | grep $1 | awk '{ print $1 }' | grep $1 )
# Checks for pid in "ps" listing, field #1.
# Then makes sure it is the actual process, not the process invoked by this script.
# The last "grep $1" filters out this possibility.
#
#    pidno=$( ps ax | awk '{ print $1 }' | grep $1 )
#    also works, as Teemu Huovila, points out.

if [ -z "$pidno" ]  #  If, after all the filtering, the result is a zero-length string,
then                #+ no running process corresponds to the pid given.
  echo "No such process running."
  exit $E_NOSUCHPROCESS
fi  

# Alternatively:
#   if ! ps $1 &#62; /dev/null 2&#62;&#38;1
#   then                # no running process corresponds to the pid given.
#     echo "No such process running."
#     exit $E_NOSUCHPROCESS
#    fi

# To simplify the entire process, use "pidof".


if [ ! -r "/proc/$1/$PROCFILE" ]  # Check for read permission.
then
  echo "Process $1 running, but..."
  echo "Can't get read permission on /proc/$1/$PROCFILE."
  exit $E_NOPERMISSION  # Ordinary user can't access some files in /proc.
fi  

# The last two tests may be replaced by:
#    if ! kill -0 $1 &#62; /dev/null 2&#62;&#38;1 # '0' is not a signal, but
                                      # this will test whether it is possible
                                      # to send a signal to the process.
#    then echo "PID doesn't exist or you're not its owner" &#62;&#38;2
#    exit $E_BADPID
#    fi



exe_file=$( ls -l /proc/$1 | grep "exe" | awk '{ print $11 }' )
# Or       exe_file=$( ls -l /proc/$1/exe | awk '{print $11}' )
#
#  /proc/pid-number/exe is a symbolic link
#+ to the complete path name of the invoking process.

if [ -e "$exe_file" ]  #  If /proc/pid-number/exe exists,
then                   #+ then the corresponding process exists.
  echo "Process #$1 invoked by $exe_file."
else
  echo "No such process running."
fi  


#  This elaborate script can *almost* be replaced by
#       ps ax | grep $1 | awk '{ print $5 }'
#  However, this will not work...
#+ because the fifth field of 'ps' is argv[0] of the process,
#+ not the executable file path.
#
# However, either of the following would work.
#       find /proc/$1/exe -printf '%l\n'
#       lsof -aFn -p $1 -d txt | sed -ne 's/^n//p'

# Additional commentary by Stephane Chazelas.

exit 0</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><A
NAME="CONSTAT"
></A
><P
><B
>Example 29-4. On-line connect status</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>#!/bin/bash
# connect-stat.sh
#  Note that this script may need modification
#+ to work with a wireless connection.

PROCNAME=pppd        # ppp daemon
PROCFILENAME=status  # Where to look.
NOTCONNECTED=85
INTERVAL=2           # Update every 2 seconds.

pidno=$( ps ax | grep -v "ps ax" | grep -v grep | grep $PROCNAME |
awk '{ print $1 }' )

# Finding the process number of 'pppd', the 'ppp daemon'.
# Have to filter out the process lines generated by the search itself.
#
#  However, as Oleg Philon points out,
#+ this could have been considerably simplified by using "pidof".
#  pidno=$( pidof $PROCNAME )
#
#  Moral of the story:
#+ When a command sequence gets too complex, look for a shortcut.


if [ -z "$pidno" ]   # If no pid, then process is not running.
then
  echo "Not connected."
# exit $NOTCONNECTED
else
  echo "Connected."; echo
fi

while [ true ]       # Endless loop, script can be improved here.
do

  if [ ! -e "/proc/$pidno/$PROCFILENAME" ]
  # While process running, then "status" file exists.
  then
    echo "Disconnected."
#   exit $NOTCONNECTED
  fi

netstat -s | grep "packets received"  # Get some connect statistics.
netstat -s | grep "packets delivered"


  sleep $INTERVAL
  echo; echo

done

exit 0

# As it stands, this script must be terminated with a Control-C.

#    Exercises:
#    ---------
#    Improve the script so it exits on a "q" keystroke.
#    Make the script more user-friendly in other ways.
#    Fix the script to work with wireless/DSL connections.</PRE
></FONT
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="PROCWARNING"
></A
></P
><DIV
CLASS="WARNING"
><P
></P
><TABLE
CLASS="WARNING"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/warning.gif"
HSPACE="5"
ALT="Warning"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>In general, it is dangerous to
	 <EM
>write</EM
> to the files in <TT
CLASS="FILENAME"
>/proc</TT
>, as this can corrupt the
	 filesystem or crash the machine.</P
></TD
></TR
></TABLE
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN19180"
HREF="procref1.html#AEN19180"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Certain system commands, such as
	     <A
HREF="system.html#PROCINFOREF"
>procinfo</A
>,
	     <A
HREF="system.html#FREEREF"
>free</A
>,
	     <A
HREF="system.html#VMSTATREF"
>vmstat</A
>,
	     <A
HREF="system.html#LSDEVREF"
>lsdev</A
>,
	     and <A
HREF="system.html#UPTIMEREF"
>uptime</A
>
	     do this as well.</P
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